Can I somehow delete Munchkin cookies for anonymous leads?

Because two details of Marketo’s anonymous lead tracking functionality violate German privacy laws, I changed the munchki code on all our web pages (incl. our landing pages) to prevent anonymous tracking. Formerly set tracking cookies for anonymous leads are still out there. So new web activity for anonymous leads shows up in Marketo and in Sales Insight. This should stop.

To prevent this I would have to delete all Marketo tracking cookies – but only for anonymous leads. Is there an easy way to detect if a visitor with a Marketo tracking code is a known lead or not just based on the cookie’s stored value? Or is there no alternative to the complicated way of using an API call to check if it’s a known lead or not?